The DNAs of a series of different chemically induced and spontaneously arising tumors have been applied to NIH3T3 mouse fibroblast cultures and observed to elicit foci of transformed cells. These transformed recipient cells thus have acquired a transmissible gene for transformation present in the donor cell from which the DNA was prepared. These cells can be placed in syngeneic mice, in which they induce fibrosarcomas. Sera from these mice can then be used to immunoprecipitate antigens present in the transfected cells. One of these antigens may be the transforming protein encoded by the transforming gene. Such experiments have led to the detection of a protein induced specifically by the transforming genes of rat neuroblastomas. This work is designed to determine whether this induced protein is encoded by the transformed gene and to examine the biochemical and enzymatic properties of the tumor protein. In addition, other experiments have led to the identification of a series of 21,000 dalton proteins encoded by several human tumor oncogenes. Experiments are under way to ascertain the role of these various oncogene proteins in the induction of the transformed phenotype.